The BRAF oncoprotein functions through the transcriptional repressor MAFG to mediate the CpG Island Methylator phenotype
Program in Gene Function and Expression; Program in Molecular Medicine; Department of Pathology
Cancer Biology | Molecular Biology | Molecular Genetics
Most colorectal cancers (CRCs) containing activated BRAF (BRAF[V600E]) have a CpG island methylator phenotype (CIMP) characterized by aberrant hypermethylation of many genes, including the mismatch repair gene MLH1. MLH1 silencing results in microsatellite instability and a hypermutable phenotype. Through an RNAi screen, here we identify the transcriptional repressor MAFG as the pivotal factor required for MLH1 silencing and CIMP in CRCs containing BRAF(V600E). In BRAF-positive human CRC cell lines and tumors, MAFG is bound at the promoters of MLH1 and other CIMP genes, and recruits a corepressor complex that includes its heterodimeric partner BACH1, the chromatin remodeling factor CHD8, and the DNA methyltransferase DNMT3B, resulting in hypermethylation and transcriptional silencing. BRAF(V600E) increases BRAF/MEK/ERK signaling resulting in phosphorylation and elevated levels of MAFG, which drives DNA binding. Analysis of transcriptionally silenced CIMP genes in KRAS-positive CRCs indicates that different oncoproteins direct the assembly of distinct repressor complexes on common promoters.
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Citation:Mol Cell. 2014 Sep 18;55(6):904-15. doi: 10.1016/j.molcel.2014.08.010. Link to article on publisher's site
Fang, Minggang; Ou, Jianhong; Hutchinson, Lloyd; and Green, Michael R., "The BRAF oncoprotein functions through the transcriptional repressor MAFG to mediate the CpG Island Methylator phenotype" (2014). Program in Gene Function and Expression Publications and Presentations. 259.